"Thirteen Conversations About One Thing" is about one thing  structure. Its four interlocking stories rarely emerge from a low-key rut, but the way the film is constructed is a mind-teaser that becomes clear only in the very last scene.

The "one thing" that everybody's talking about in the movie's title is the subject of happiness, and yet it's not clear that we've learned much about happiness by the end of this didactic piece. It tries hard to be a great, deep, thoughtful film, and it isn't bad at all but it comes up well short of greatness.

Surprisingly, a cast full of consistently fine actors fails to breathe adequate life into the film, maybe because the script lacks warmth or maybe because this is the effect that writer-director Jill Sprecher was going for. The lighting is dim, the mood is gloomy, and the ideas are not as interesting as you would hope.

Even Alan Arkin doesn't fully flesh out his rather one-dimensional character, an office boss who wants his employees to share his misery but is stymied by a subordinate who remains perpetually upbeat in spite of his best efforts. We also have Matthew McConaughey as a stereotyped yuppie prosecutor whose pomposity is shaken when he hits a young house cleaner (Clea Duvall) with his luxury car. And John Turturro barely has a pulse as an emotionally inept professor who's tired of his wife (Amy Irving) and looking for a little excitement.

If the direction and the acting fail "Thirteen Conversations," at least there's the puzzle of how these stories intersect  and when. In fact, they are only lightly connected to each other and to the idea of happiness, but at least the ending will reward you with a little light bulb going off in your head if you're alert to the clues.